I'm getting flashing/flickering trees and skylines in Conan Exiles with my Powercolor R9 390 using 18.7.1 drivers.. Despite the different AMD hardware, this video, at the 23 second mark, shows exactly what I'm seeing.
This one, at the 7 second mark, also shows exactly what I'm seeing: Conan Exiles RX Vega 64 - 18.6.1 Driver Test - YouTube
The issue is most prevalent in the jungle region in the southeastern game world, the swamp a hair north of that, and the green highlands to the far north (where the above videos are). Especially when raining in-game. Note that if you are trying to reproduce this issue, just logging into the starting desert region is not a sufficient, appropriate test. I haven't observed the issue often there. You really need to travel your character to the aforementioned regions (admin controls/ admin panel can accelerate the trip for testing purposes).
My game graphics settings are set to auto, which has everything set to high. I am using a freesync 34" LG 2560x1080 and freesync is enabled on both the monitor and the drivers.
The issue is also being reported by AMD video card users on the steam forums:
Powercolor R9 390 8GB (AXR9 390 8GBD5-PPDHE) w/ 18.7.1 drivers.
LG 34UM61-P 34" 2560x1080 Freesync monitor
Asus Z77 Deluxe - latest bios
Windows 10 64 bit - latest updates
16GB of ram
700+ watt Corsair PSU
Latest steam version of Conan Exiles running on a dedicated g-portal server. No mods.
Edit: Attached my dxdiag.